1. Field of the Invention
This invention relates to the orthopedic medicine art and more particularly to pressure detection arrangements for indicating the pressure between limbs, or other portions of the body, and casts applied thereto.
2. Description of the Prior Art
In order to immobilize a limb, or other body portion, having a fractured bone, or for other purposes a cast is often applied to the exterior surface of the limb or body portion to hold, for example, the limb in a position which will facilitate healing of the internal bone structure. The application of an excessively tight cast or internal inflammation or swelling of the limb or body portion under the cast may cause swelling and press against the cast. Gangrene or other deleterious effects may then result from the obstruction of the blood vessels, or otherwise, due to the pressure of the cast.
In the past only the indication of swelling of the limb at the exterior end of the cast or the discomfort of the patient provided information to the physician that abnormal conditions existed within the cast. Failure to take prompt action often resulted in the loss of a limb or loss of life.
Several devices or elements of devices have been developed to detect pressure and temperature abnormalities in medical situations. U.S. Pat. No. 3,958,567 discloses a reservoir inserted between the brain and the skull attached to a tube passing through a hole in the skull for connection to a fluid pressure sensing device. A radiographic fluid is added to the system to transmit the internal pressure to the external measuring instrument. No continuous reading, independent direct pressure indication is given by the reservoir and tube alone.
U.S. Pat. No. 3,967,579 discloses a temperature sensitive device for indicating spoilage of chemical or food products after exposure for a predetermined time period to a particular predetermined temperature. As the temperature exceeds the predetermined value, a diffusion barrier permits diffusion of the temperature sensitive material onto an indicator, which causes a color change in the indicator.
U.S. Pat. No. 3,853,118 discloses two pressure sensing devices which measure the stretching of the skin, such as during an intravenous injection, by use of a conventional strain gauge or a sealed, liquid-filled capsule attached to a pressure transducer. Both require external sensing instruments.
U.S. Pat. No. 3,699,094 discloses a catheter for use with an external fluid pressure sensing device to measure intracranial pressures.
U.S. Pat. No. 3,613,679 discloses an elastic bandage which has different shaped designs imprinted thereon and the change in the size of the design while wrapping the bandage is an indication of the tension that is applied.
None of the above patents show a direct reading pressure sensitive device which may be utilized within a cast to provide a continuous, independent indication or measurement of the pressure existing between the cast and the portion of the body encased by the cast.